Wheaten maran pullet with respiratory infection?

[StarLover21]

I have a wheaten maran pullet (under laying age), who I beleive has a respiratory infection. One of my other chickens has had this same problem in the past, and we gave her Tylan50 and she recovered in no time. What I'm wondering is how much do we give her? She's 21 weeks, but small for her age, nowhere near laying age. She's smaller than my white leghorn by far.


Thanks!